An Australian coach is convinced that getting splashed by the dirty water gave him a rash on his ankle. Sailor health seems to be the main concern, from the AP:

"Health experts haves suggested that sailors be vaccinated for hepatitis A, and at a small regatta last year sailors rubbed alcohol on their hands after leaving the water."

Mat Belcher, a 2012 gold medalist, told the Brazilian paper Folha de São Paulo (via AFP), "We found a lot of plastic bottles and bags. Yesterday we saw a dead dog in the water. If the Olympics were tomorrow, we would really have a problem."

Health risks aside, a big worry is that large chunks of debris — sofas and other pieces of furniture have been seen in the bay — will disrupt the event. Organizers have sent out clean-ups boats (basically water trash trucks) to take care of these potential obstacles:

Buda Mendes/Getty Images

The conditions are worst at the shores of the bay. Australian sailor Nikolaus Resch told the AP that the bay smells like raw sewage at low tide.